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Seasonal cycling in carbon, alkalinity, and nutrients in landfast sea ice in Hangar Cove, Adelaide Island, West Antarctic Peninsula, were investigated during winter, spring, and summer 2014–2015. Temporal dynamics were driven by changes in the sea‐ice physicochemical conditions, ice‐algal community composition, and organic matter production. Winter sea ice was enriched with dissolved inorganic carbon (DIC) and inorganic nutrients from organic matter remineralization. Variations in alkalinity (Alk) and DIC indicated that abiotic calcium carbonate (ikaite) precipitation had taken place. Relative to other nutrients, low phosphate (PO4) concentrations potentially resulted from co‐precipitation with ikaite. Seawater flooding and meltwater induced variability in the physical and biogeochemical properties in the upper ice in spring where nutrient resupply supported haptophyte productivity and increased particulate organic carbon (POC) in the interstitial layer. Rapid nitrate (NO3) and DIC (< 165 μmol kg−1) uptake occurred alongside substantial build‐up of algal biomass (746 μg chlorophyll a L−1) and POC (6191 μmol L−1) during summer. Silicic acid drawdown followed NO3 depletion by approximately 1 month with a shift to diatom‐dominated communities. Accumulation of PO4 in the lower ice layers in summer likely resulted from PO4 released during ikaite dissolution in the presence of biofilms. Increased Alk : DIC ratios in the lower ice and under‐ice water suggested that ikaite dissolution buffered against meltwater dilution and enhanced the potential for atmospheric CO2 uptake. This study revealed strong seasonality in carbon and nutrient cycling in landfast sea ice and showed the importance of sea ice in biogeochemical cycling in seasonally ice‐covered waters around Antarctica. [ABSTRACT FROM AUTHOR]

The general aim of this work was to compare the leaf-level responses of different protective components to water deficit and high temperatures in Quercus cerris L. and Quercus robur L. Several biochemical components of the osmotic adjustment and antioxidant system were investigated together with changes in hormones. Q. cerris and Q. robur seedlings responded to water deficit and high temperatures by: (1) activating a different pattern of osmoregulation and antioxidant mechanisms depending on the species and on the nature of the stress; (2) upregulating the synthesis of a newly-explored osmoprotectant, dimethylsulphoniopropionate (DMSP); (3) trading-off between metabolites; and (4) modulating hormone levels. Under water deficit, Q. cerris had a higher antioxidant capacity compared to Q. robur, which showed a lower investment in the antioxidant system. In both species, exposure to high temperatures induced a strong osmoregulation capacity that appeared largely conferred by DMSP in Q. cerris and by glycine betaine in Q. robur. Collectively, the more stress-responsive compounds in each species were those present at a significant basal level in non-stress conditions. Our results were discussed in terms of pre-adaptation and stress-induced metabolic patterns as related to species-specific stress tolerance features. [ABSTRACT FROM AUTHOR]

Coastal zones of Antarctica harbor rich but highly variable phytoplankton communities. The mechanisms that control the dynamics of these communities are not well defined. Here we elucidate the mechanisms that drive seasonal species succession, based on algal photophysiological characteristics and environmental factors. For this, phytoplankton community structure together with oceanographic parameters was studied over a 5‐year period (2012–2017) at Rothera Station at Ryder Bay (Western Antarctic Peninsula). Algal pigment patterns and photophysiological studies based on fluorescence analyses were combined with data from the Rothera Time‐Series program. Considerable interannual variation was observed, related to variations in wind‐mixing, ice cover and an El Niño event. Clear patterns in the succession of algal classes became manifest when combining the data collected over the five successive years. In spring, autotrophic flagellates with a high light affinity were the first to profit from increasing light and sea ice melt. These algae most likely originated from sea‐ice communities, stressing the role of sea ice as a seeding vector for the spring bloom. Diatoms became dominant towards summer in more stratified and warmer surface waters. These communities displayed significantly lower photoflexibility than spring communities. There are strong indications for mixotrophy in cryptophytes, which would explain much of their apparently random occurrence. Climate models predict continuing retreat of Antarctic sea‐ice during the course of this century. For the near‐future we predict that the marginal sea‐ice zone will still harbor significant communities of haptophytes and chlorophytes, whereas increasing temperatures will mainly be beneficial for diatoms. [ABSTRACT FROM AUTHOR]

The Southern Ocean is a hotspot of the climate-relevant organic sulfur compound dimethyl sulfide (DMS). Spatial and temporal variability in DMS concentration is higher than in any other oceanic region, especially in the marginal ice zone. During a one-week expedition across the continental shelf of the West Antarctic Peninsula (WAP), from the shelf break into Marguerite Bay, in January 2015, spatial heterogeneity of DMS and its precursor dimethyl sulfoniopropionate (DMSP)was studied and linked with environmental conditions, including sea-ice melt events. Concentrations of sulfur compounds, particulate organic carbon (POC) and chlorophyll a in the surface waters varied by a factor of 5-6 over the entire transect. DMS and DMSP concentrations were an order of magnitude higher than currently inferred in climatologies for the WAP region. Particulate DMSP concentrations were correlated most strongly with POC and the abundance of haptophyte algae within the phytoplankton community, which, in turn, was linked with sea-ice melt. The strong sea-ice signal in the distribution of DMS(P) implies that DMS(P) production is likely to decrease with ongoing reductions in sea-ice cover along the WAP. This has implications for feedback processes on the region's climate system. This article is part of the theme issue 'The marine system of the West Antarctic Peninsula: status and strategy for progress in a region of rapid change'. [ABSTRACT FROM AUTHOR]

The pigment composition of Phaeocystis antarctica was monitored under various conditions of light, temperature, salinity, and iron. 19′- Hexanoyloxyfucoxanthin ( Hex-fuco) always constituted the major light-harvesting pigment, with remarkably stable ratios of Hex-fuco-to-chl a under the various environmental conditions. Increased pigment-to-chl a ratios at low irradiance confirmed the light-harvesting function of Fucoxanthin ( Fuco), 19′- Hexanoyloxy-4-ketofucoxanthin ( Hex-kfuco), 19′-butanoyloxyfucoxanthin ( But-fuco), and chl c2 and c3. Increased pigment-to-chl a ratios at high irradiance, low iron concentrations, and to a lesser extent at high salinity confirmed the photoprotective function of diadinoxanthin, diatoxanthin, and ß,ß-carotene. Pigment ratios were not always according to expectations. The consistent increase in But-fuco/chl at high temperature, high salinity, and low iron suggests a role in photoprotection rather than in light harvesting. Low Hex-kfuco/chl ratios at high salinity were consistent with a role as light harvester, but the high ratios at high temperature were not, leaving the function of Hex-kfuco enigmatic. Dedicated experiments were performed to test whether or not the light-harvesting pigment Fuco could be converted into its structural relative Hex-fuco, and vice versa, in response to exposure to light shifts. Rapid conversions could not be confirmed, but long-term conversions cannot be excluded. New pigment ratios are proposed for chemotaxonomic applications. The ratios will improve pigment-based diagnosis of algal species in waters dominated by P. antarctica. [ABSTRACT FROM AUTHOR]

Ocean dimethylsulfide (DMS) produced by marine biota is the largest natural source of atmospheric sulfur, playing a major role in the formation and evolution of aerosols, and consequently affecting climate. Several dynamic process-based DMS models have been developed over the last decade, and work is progressing integrating them into climate models. Here we report on the first intemational comparison exercise of both 1 D and 3D prognostic ocean DMS models. Four global 3D models were compared to global sea surface chlorophyll and DMS concentrations. Three local 1D models were compared to three different oceanic stations (BATS, DYFAMED, OSP) where available time series data offer seasonal coverage of chlorophyll and DMS variability. Two other ID models were run at one site only. The major point of divergence among models, both within 3D and 1D models, relates to their ability to reproduce the summer peak in surface DMS concentrations usually observed at low to mid- latitudes. This significantly affects estimates of global DMS emissions predicted by the models. The inability of most models to capture this summer DMS maximum appears to be constrained by the basic structure of prognostic DMS models: dynamics of DMS and dimethylsulfoniopropionate (DMSP), the precursor of DMS, are slaved to the parent ecosystem models. Only the models which include environmental effects on DMS fluxes independently of ecological dynamics can reproduce this summer mismatch between chlorophyll and DMS. A major conclusion of this exercise is that prognostic DMS models need to give more weight to the direct impact of environmental forcing (e.g., irradiance) on DMS dynamics to decouple them from ecological processes. [ABSTRACT FROM AUTHOR]

We report data of a naturally occurring radionuclide, 234Th, an in situ tracer, to investigate vertical export of biogenic matter during a vernal bloom of Phaeocystis pouchetii in the fjords of northern Norway. To optimise sampling of different stages of the bloom, three fjords with increasing oceanic influence (Balsfjord, Malangen fjord and Ullsfjord, respectively) were investigated in April 1997. Contrasting situations were encountered between the three fjords: the proliferation of P. pouchetii in Ullsfjord surface waters coincided with a drastic reduction of particulate 234Th fluxes in traps, although particulate organic carbon (POC) and dimethylsulphoniopropionate (DMSP) were exported and 234Th was available in surface waters. When large colonies make up a significant fraction of the vertical flux, as observed in Ullsfjord in April 1997, there may be a large and rapid change in the POC/234Th ratio, further complicating the use of 234Th as a tracer for POC export. The results suggest that the proliferation of Phaeocystis pouchetii during vernal bloom could temporary increase OC/234Th ratio of particles and delay the particulate export of 234Th, and probably of other particle-reactive species, from surface waters. [ABSTRACT FROM AUTHOR]

The production of the secondary metabolite dimethylsulfoniopropionate (DMSP) by marine microalgae has a strong impact on the global sulfur cycle, as DMSP is the precursor of the climate active gas dimethylsulfide. Quantifying the impact of abiotic parameters on DMSP production is needed to accurately depict DMSP production in ecosystem models. In this study, we investigated if de novo production of DMSP was upregulated under short‐term elevated irradiance and ultraviolet A radiation (UVA‐R). We exposed high‐light and low‐light acclimated cultures of Emiliania huxleyi, Tetraselmis sp., Thalassiosira oceanica, and Phaeodactylum tricornutum to high irradiance and UVA‐R treatments and followed de novo DMSP production and carbon fixation. We show that combined photosynthetically active radiation and UVA‐R resulted in increased net photoinhibition rates, but decreased specific DMSP production and growth compared to non‐UVA‐R treatments for all species. Photoacclimation to high photosynthetically active radiation resulted in a decreased UVA‐R sensitivity and positively affected the DMSP‐to‐carbon concentration ratios within the cultures. We conclude that there is no active short‐term upregulation of DMSP production under elevated photosynthetically active radiation and UVA‐R. Instead, the production of DMSP in response to light‐stress is closely coupled to particulate organic carbon production in all cases. While the relatively high cellular concentrations of DMSP do not exclude a de facto antioxidant function, its production is likely regulated by other cellular processes, for example, an overflow mechanism. The data of this study aim to improve the mechanistic understanding of DMSP synthesis, as well as to quantify DMSP production rates in different marine phytoplankton species. [ABSTRACT FROM AUTHOR]

Part II. Discusses the isolation and culture of a strain of Antarctic Phaeocystis specie, Prymnesiophyceae, under iron- and light-limited conditions. Cellular content of chlorophyll; Accessory light-harvesting pigments; Photoprotective cycle of diato/diadinoxanthin.

Part I. Examines the biochemical composition of an Antarctic Phaeocystis specie strain, Prymnesiophyceae, to determine whether iron limitation would result in energy stress or induced nitrogen deficiency. Importance of iron in phytoplankton growth; Intracellular production of dimethylsulfoniopropionate; Tricarboxylic acid cycle.